Antenna system



Feb. 17, 1931. J STERBA 1,792,662

ANTENNA SYSTEM Filed March 31., 1925 Patented Feb. 17, 1931 nnNEsT J. swan-BA, on NEW YO K, N. Y.,

ASSIGNOR, BY MESNE ASSIGNMENTS, TO

VTESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK ANTENNA SYSTEM 7 Application filed March 31, 1925. Serial No. 19,574.

' This invention relates to an antenna system, and more particularly to a multiple antenna. It has heretofore been proposed to arrange a plurality of antenna sections in a single line, the sections being connected together in succession to constitute an array having a primary section and a plurality of secondary sec tions, all of which operate as radiators. Each section is connected to ground through a lead including a loading coil for controlling its tuning, and high frequency energy is supplied at relatively low voltage to the primary section which operates as a step-uptransformer supplying the energy to the secondary sections.

The loading coilsincluded in the down leads of the secondary sections each serve to neutralize a portion of the capacity of the antenna'section with which it is associated, while theloading coil in the primary section down lead is designedto'neutralize the capacity of this section and, in addition, the

. remainder of the capacity of the secondary sections which isnot neutralized by the loading coils associated with them. In certain instancesthe capacity thus neutralized is considerably greater than that of any one section of the system. The purposes of this unsymmetrical loading of the different sections is to render the primary section a tuned radiating unit of low impedance for connecting a high frequency source to the secondary radiating sections The loading coils associated with the different secondary antenna sections are of such relative values that the capacity of these sections is equally distributed among the down leads and a current node is created upon each fiat top section.

.With this arrangement, in order to change over'from one frequency to another, of several frequencies which may be efficiently radiated by the system, the loading coil of'each section must be adjusted separately. Because of the physical arrangement of the sections, such adjustment involves a large amount of laborand loss of considerable time, or, if a quick change-over is to be effected, a large personnel is required for this purpose.

The present invention 1s: directed to a multiple antenna having the sections symmetrically disposed about a geometrical center, whereby there is effected a material saving in the labor and time required to change the tuning of the antenna.

In accordance with this invention a plurality of antenna sections are symmetrically arranged relatively toa geometrical center to constitute a system. Similar terminals of the sections are connected together to provide a common terminal which is connected to ground through a down lead including a loadadapted to neutralize the remaining parts of the capacities of the antenna sections with which they are associated.

In this arrangement the capacity of any one secondary section is considerably in excess of the capacity of the primary section and therefore the high frequencyenergy is substantially concentrated in the secondary sections, so that the common down lead constitutes, in effect, a non-radiating primary antenna section for tuning the array to the frequency of the wave to be radiated. The tuning'of the antenna array can therefore/be controlled by adjusting the loading coil in the common down lead, or primary antenna section, so that by a single operation a quick changeover from one frequency to another may be effected.

One object of the invention is to simplify the operation whereby the tuning of a multiple antenna may be controlled.

Another object is to considerably reduce the labor and time required to change the tuning of an antenna array.

'A further ob 'ect is to render the tuning of an antenna array controllable by a single operation.

A. feature of the invention is a single means The grounded terminals of the'down.

for controlling the tuning of a multiple antenna system.

An additional feature is an antenna array with means whereby the high frequency current and voltage supplied to the radiating sections are substantially in phase with each other.

For a complete understanding of the invention both as to its organization and mode of operation, reference may be made tothe following description read in conjunction with the attached drawing in which Figs. 1, 2 and 3 show antenna systems embodying the invention; and Fig. 4 illustrates a detail of the system, whereby a uniform mechanical tension or strain is maintained in the different antenna sections.

Referring now to Fig. 1 there is shown an antenna system comprising a plurality of flat top sections 1, 2 and 3. Section 1 consists of portions a and 6. section 2 of portions 0 and cl, and section 3 of portions 0 and f.

The antenna supporting structure comprises towers 4, 5 and 6 disposed at the apices of an equilateral triangle, between which are supported two port-ions of different antenna sections to constitute the sides of the triangle. Thus a and c of sections 1 and 2, respectively, are supported betwcentewers 4 and 5, (Z and 6 between towers 5 and G, and f and 7) between towers 6 and 4. The flat top portions of the antenna system are connected to the towers 4, 5 and 6 by messenger cables which include insulators 20.

Similar terminals of sections 1, 2 and 3 are connected together by conductors 7, 8 and 9 extending to a common terminal to which is connected a down lead 10 including a loading coil 11 having associated with it an adjustable contact 12 connected to ground. The

other terminals of section 1 are connected to ground through down lead 42 which includes a loading coil 13. In a similar manner the opposite terminals of sections 2 and 3 are re spectively connected to ground by down leads 14 and 15, each of which includes a loading coil 13. The ground system is made more effective-by conductors 16 interconnecting the several ground points of coils 13 with the ground at contact 12.

In accordance with the present invention the coils 11 and 13 are designed so that the different sections and the system are tuned to the frequency of the wave to be radiated, but the inductance of coils 13 relatively to that of coil 11 is such that, when the elec tromotive force of the high frequency wave supplied to the system is maintained constant, the capacity of the down leads 42, 14 and 15 will be greater than that of the down lead 10. The relative values of the inductance in the coils 13 and 11 are such that current nodes occur at or near the down lead 10, or even in proximity to the upper terminal of the loading coil 11, with the result that the current flowing through the down lead 10 Will be small, while the currents flowing through the down leads 42, 14 and 15 will be large. A source of high frequency energy 17 is coupled to the array through he coil 11 included in the common down lead 10. Source 17 may comprise any well known arrangement for supplying high frequency signal modified waves to the antenna.

By adjusting the loading coil in the down lead 10, the tuning of the sections of the system may be varied with the result that the high frequency current nodes are shifted inwardly or outwardly along the flat top portions of the antenna sections.

In one test it was found that the current flowing through the primary section 10 was approximately one-tenth to oneethirtieth of that traversing the secondary sections when the energy supplied to the array was varied from 285 kilocycles to 235 kilocycles, respectively, so that for all frequencies used the former is a non-radiating unit, while the lattcr operate as radiators.

Fig. '2 illustrates an antenna system similar to that shown in Fig. 1. Like elements in the twofigures are-identified'by like reference characters. This system dilfers from that described above in that the portions of the different antenna sections are connected together to constitute one side of the triangular figure. Thus portions a and b of section 1 are supported between towers 4 and 5, portions 0 and (Z of section 2 between towers 5 and'G, and portions 6 and fof sect-ion 3between towers 6 and 4.

The common down lead 10 is connected by conductors 7, 8 and 9, respectively, to

the junction points of portions ab, 0-01 and cf. The individual down leads 42, 1'4 and 15 are also connected to these'junction points respectively.

The common down lead 10 is provided with a loading coil '11 and the individual down leads 42, 14 and 15 are provided with loading 1 tion by the lines m, 2 and 2. In this case the F inductance 11 is adjusted so that a current anti-node occurs 1n proxnnity to the c011 11 and a current node occurs on the primary section in proximity to the common junction points of the portions ab of section 1.

he current is distributed in sections 2 and 3 in a similar manner. This arrangement operates in a manner similar to that shown in Fig. 1. Its tuning may be controlled by adjusting the contact 12 associated with the loading coil-11, whereby the current node is shifted inwardly oroutwardly upon the an of double fan-shaped sections 21 supported by messenger cables 22 secured to towers 4, and 6. Each section is insulated from the towers by insulators included in the messenger cables 22 and the unlike, or outer, terminals are connected to auxiliary supporting towers 23 by messenger cables 24;, each including an insulator 25. V I I Y The antennasections radiate from a common center which ,is connected through a down leadlO, inductance coilll, and ad,

- justable contact 12 "associated therewith to 7 ground. The other terminals of the sections are grounded through down leads 26,. each including'a loadingcoil 13. The grounded ends of the coils 13 and the contact 12, associated with'coil 11, are connected together by aground system 27 While thesystem 27 is indicated as a single conductor extenda common groundl'ead28 to which the contact 12 is connected, it is to be understood that this is merely a bus bar which maybe connected to' any well known design of systern for providingthe desired low resistance connection to ground.

5: I The inductance of the loading coil '11 in down lead 10 and the inductance'of the coils 13 in down leads 26 should be so designed that the high frequency energy is distributed in the antennasections in amanner similar to that described in connection wlththe preceding figures.

The antenna system of 3 operates and may be controlled. in the same manner as those previously described. Thus by adjusting the loading coil 11 the tuning of the system may be changed so that it is resonant to a difl'e'rent frequency and the current nodal I cluded in a section, which were then permanently secured to the supporting masts or towers. In another arrangement the terminals of the sections were connected by supporting cables to a winch or hoisting mechanism which was used to raise the antenna system into position between the towers and to apply the desired mechanical strain to each section. 3

In either case, there is considerable liability during stormy weather, for some portion or the whole of the antenna system tobreak,

thereby causing serious interruption of service. In order to overcome this objectionable feature, there is illustrated in Fig. 4 an arrangement which may be used to maintain uniform the mechanical tension applied to the different sections of theantenna system.

The supporting cable for an antenna wire or section is led over a block or pulley30,

at or near the top 'of each supporting tower,

and has its opposite end connected to a pulley or block 31. A- control cable 32 is connectedat one end'to aweight 33, which slides freely'in the frame 34:. The cable 32 passes over apulley35, secured to the frame'34, the sheaf-of pulley31,-ove'r a'pulley 36 and has its other end connectedto a winch 37 mounted on the tower in proximity-to the ground. 1

With the controlling mechanism in the position shown, the strainapplied to the antenna unit will be determined by the weight 33.. Any expansion or contraction of the an tenna unit, oradditional load applied thereto, will cause the weight 33 to change its position so as to maintain uniform the tension applied to the unit. Thus during wind ing from the lower terminals of coils 13 to or sleet storms, the strain applied to the condu'ctors constituting the antenna unit or section is limited tof that determined by the weight as. j a

This control'mechan'ism' may be used'with any of the antenna systemsdescribed above,

and for purposes of illustration is shown applied to the antenna system of Fig. 2. In

' proximity to the supporting towers the messenger cables for adjacent antenna portions are'connected together and to a supporting .cable,"which after passing over theblock 30,

is connectedtothe pulley 31. The control cables 32 have their ends respectively con nected to the weight 33 and'l-winch 37 in each case.

An antenna system similar to that-shown in Fig. 3 has been operated for a frequency range from 235 to 285 kilocycles.

The supporting structure consisted of selfsupporting towers 165 feet high and 500 feet apart. The static capacityof the antenna with all of the down leads open was 5,375

mmf. The inductance of each of the coils in the down leads individual to the sections varied from .22 to .32 millihenries for the frequency rangegiven above, and the inductance of the coil included in the common down lead was 1.2 millihenries. The tuning of this system was also controlled by varying the inductance of the common down lead, while maintaining constant the inductance of the coils included in the individual down leads. In either case the resonance of the system was varied from 235'kilocycles to 285 kilocycles without materially affecting the radiating characteristic of the system.

The lines 02, y and 2, applied to the system tions at high voltage and low current.

of Fig. 2, to illustrate the current distribution in section 1 of the antenna system, serve to identify the current distribution in each of the sections of this system, as well as in that of each section of the antenna systems shown number of secondary sections connected by a low impedance primarysection to the secondary of a step-up transformer; by means of which the signal wave source is coupled to the antenna. The primary of this transformer may or may not be tuned by a shunt condenser to the frequency of the waves supplied by the source. The primary'section or common down lead is then only a short low impedance transmission line over which high frequency energy is supplied to a loadicircuit comprising a plurality of secondary sections connected in parallel.

Under the conditions noted above the phase angle between the currents, supplied to the primary section with reference to the voltage across the secondary and the coupling transformer, decreases as the number of turns of the transformer secondary is increased. Under ideal conditions, the current traversing the primary section and the voltage across the transformer secondary would be in phase. However, in practice the phase angle between the primary section current and the primary section Voltage is only approximately zero.

This method of supplying high frequency energy to an antenna system may be defined as high voltage feed, and serves to determine one limit of the frequency range over which the antenna system described above is operable. The other frequency limit is determined by the case in which the current in the antenna primary section is in phase quadrature with the voltage applied thereto.

Over thefrequency range identified by these limits, the primary current decreases in magnitude as the high voltage feed condition is approached. When this is obtained, current flowing through the antenna primary section is extremely small and is approximately equal to that necessary to provide energizing current to the radiating system. In other words the magnitude of the current transmitted through the antenna primary section is approximately that necessary to take care of the power loss in the radiating system. This loss is determined by the equation where I is the current and W is the loss due to R, the multiple impedance of the secondary sections.

In the arrangements herein described, the antenna system is illustrated as triangular. However, the antenna system may be composed of any number of sections symmetrical ly disposed about a geometrical center. The down loads may comprise cage sections or single conductors. The flat top portions of the antenna sections may be of the cage type or may consist of a plurality of conductors in a single plane or arranged in any other suitable manner.

While in the foregoing, specific details have been described for the purpose of completely and clearly disclosing the nature of the invention, it is to be understood that this invention is not limited thereto, but only by the scope of the attached claims.

What is claimed is:

' 1. A multiple-tuned radiating system comprising a plurality of antenna sections symmetrically disposed about a geometrical center, and a ground connection therefor comprising a down lead common to said sections and other down leads comprising one individual to each of said sections.

2. A radiating system comprising a plurality of antenna sections symmetrically disposed about a geometrical center, and a ground connection therefor comprising a down lead common to said sections and other down leads individual to said sections, said common down lead operating as a non-radiating high voltage source for supplying energy at approximately the voltage antinode to the symmetrical sections.

3. A radiating system comprising a plurality of antenna sections symmetrically disposed about a geometrical center, a ground connection therefor comprising a down lead common to said sections and other down leads individual to said sections. and means included in said common down lead for shifting the voltage anti-node inwardly or outwardly on the symmetrical sections, whereby the resonant frequency of the system may be changed.

4:. A multiple-tuned radiating system comprising a plurality of antenna sections symmetrically disposed about a geometrical center, a ground connection therefor comprising a down lead common to said sections and other down leads comprising one individual to each of said sections, and means included in at least one of said down leads for controlling the tuning of said sections.

5. A radiating system comprising a plurality of antenna sections symmetrically disposed about a geometrical center, a ground connection therefor comprising a down lead common to said sections and other down leads individual to said sections, reactances included in the respective down leads for deter mining the electrical characteristics of said sections, the reactance included in one section being adapted to neutralize the reactance of different character inherent in said section and also reactance of an equaland symmetrically disposed portion of ,each-ofthe other sections. U 6. A radiating system comprising a plurality of antenna sections symmetrically disposed about a geometrical center, a ground connection therefor comprlslng a down lead common to said sections and other down leads individual to said sections, loadingcoils included in the respective down leads for determining the electrical characteristics of said section, the loadin coil in one section being adapted to neutrallze the capacity of the section in which it is included and the capacity of an equal and symmetrically disposed por tion of each of the other sections.

7 A radiating system comprising a plurality of antenna sections symmetrically disposed about a geometrical center, a ground connection therefor comprising a down lead common to said sections and other down leads individual to said sections, and loading coils associated with said down leads for tuning said sections and the system to the frequency of the Waves to be radiated, said coils cooperating to produce a current node in proximity to the junction of said common down lead With said sections.

8. A radiating system comprising a plurality of antenna sections symmetrically disposed about a geometrical center, a ground a connection therefor comprising a down lead common to said sections and other down leads individual to said sections, a source applying a signal Wave to be radiated, loading coils included in said down leads for tuning said sections and the system to the frequency of the supplied Wave, the coil included in the common down lead being designed to cause the current and voltage produced therein by said supply source to be approximately in phase with each other.

In Witness whereof, I hereunto subscribe my name this 30th day of March, A. D., 1925.

ERNEST J. STERBA. 

